The present invention describes a family of new and unique pyrotechnic compositions, propellants based on them, and a method of preparing same. The basic compositions consist of mixtures or coprecipitates of bis-triaminoguanidinium decahydrodecaborate and triaminoguanidine nitrate, in any proportions.
A particular objective in preparing compounds suitable for certain types of pyrotechnic usage is to achieve a high gas output and low molecular weight combustion products, when the compound is burned. Combustion products such as hydrogen (H.sub.2) and nitrogen (N.sub.2) gas fulfill this requirement. In preparing salts useful as pyrotechnic monopropellants and oxidizers from an anion such as decahydrodecaborate (-2) (B.sub.10 H.sub.10.sup.-2) or nitrate (NO.sub.3.sup.-), it has been found advantageous to use a cation containing a high weight fraction of atomic nitrogen and hydrogen. The triaminoguanidinium ion, chemical formula C (NHNH.sub.2).sub.3.sup.+1, has been found to be such a cation. In addition, the corresponding Bronsted base of the ion, free triaminoguanidine, is a strong base, which imparts to the cation, and thus the salt, a high degree of chemical stability.
Triaminoguanidine nitrate, (NHNH.sub.2).sub.3 CNO.sub.3, also known to those practiced in the art as TAGN, has been found to have particular usefulness as an oxidizer in certain classes of propellants. It is by itself a slow, cool burning monopropellant with high gas output. One of the most serious drawbacks with the use of TAGN is the control of burning rate of the neat material, as well as propellants containing it.
This invention describes compositions employing TAGN as a starting material that have pyrotechnic performance superior to pure TAGN, in terms of energy and gas output and burning rate control. In particular, very fast burning, high energy propellants can be manufactured from them. The subject compositions consist of very intimate blends or coprecipitates of an ultrafast deflagrating monopropellant, namely the triaminoguanidinium salt of decahydrodecaboric acid, with TAGN. The resulting compositions, which can be prepared over a wide range of the constituent anion content, have pyrotechnic properties wholly unlike the starting salts.
Historically, boron hydride salts, in particular the nonmetal salts of decahydrodecaboric acid, has been discovered to have particular utility in the field of high energy fuels. They may be used as constituents of pyrotechnic compositions and in propellants. For example, non-metallic salts of the decahydrodecaborate ion, and exemplary uses, are disclosed in the copending application of common assignment entitled IGNITION AND PYROTECHNIC COMPOSITIONS, Ser. No. 694,625, filed June 10, 1976, now abandoned. For these compositions, in general, the ratio of decahydrodecaborate fuel to oxidizer was fixed within certain defined limits in order to achieve acceptable pyrotechnic performance.
The particular decahydrodecaborate salt used in this invention is the fully amino-substituted compound, which is disclosed in my copending patent application of common assignment entitled BIS-TRIAMINOGUANIDINIUM DECAHYDRODECABORATE AND A PROCESS FOR ITS PREPARATION, U.S. Pat. No. 4,130,585, incorporated herein by reference. In contrast to other simple decahydrodecaborate salts, the triaminoguanidine salt is a powerful monopropellant; i.e., combusts by itself releasing internal energy, without need of additional oxidizer materials. The compound is very unusual in that it contains only boron, nitrogen, carbon and hydrogen, but no oxygen.
The advantage of the chemical system formed by combining the two monopropellants is that they can be mixed in any proportion and, as well, both possess the triaminoguanidine ion as a common cation.
The preferred method of preparing a compound with a given stoichiometry consists of dissolving the two starting salts in water and rapidly precipitating the constituent ions simultaneously with a nonsolvent such as isopropanol. The detailed methodology for this process, known as "coprecipitation", has been disclosed in my copending application entitled COPRECIPITATED PYROTECHNIC COMPOSITION PROCESSES AND RESULTANT PRODUCTS, Ser. No. 694,626, filed June 10, 1976 now U.S. Pat. No. 4,135,956. This process for preparing the subject compositions makes use of the triaminoquanidinium cation which is common to both starting salts, and coprecipitates of the two salts result in very intimate mixing of the B.sub.10 H.sub.10.sup.-2 and NO.sub.3.sup.- anions which helps impart to the resulting compositions very reproducible pyrotechnic performance.